This invention relates to an automatic oil draining system for use in large turbo machinery having internal gas under pressure such as electric power generators; and more particularly to such a system utilizing (1) pressurized oil to prevent the pressurized gas from escaping to the external environment and (2) pressurized water to cool the electrical stator coils.
Hydrogen gas under pressure is commonly utilized within large electric power generators to cool the stator core and the rotor coils because of the improved cooling capabilities of hydrogen as contrasted with air. In order to keep the gas from leaking to the external environment through the bearings, oil fed hydrogen seals are utilized on the shaft adjacent to the bearings. The oil pressure within the seals is deliberately kept at a pressure higher than the gas pressure within the generator to prevent the potentially flammable and explosive hydrogen from leaking out. Since this pressure differential creates the possibility of the oil leaking through the seals into the generator, oil deflectors are provided to direct the leaked oil to an external sump for drainage. Under normal circumstances deflectors completely prevent any oil from entering the region within the generator. However, there have been instances where the deflectors were not 100% effective, allowing some leakage. Oil leakage into the internal regions of the generator can cause forced outages or shutdown of the generator if it were allowed to accumulate.
Oil entering the generator collects in the lower regions of the generator. A drain line is normally provided in the lower frame extension of the generator which houses the high voltage bushings, to collect the oil which enters the generator, along with any potential water leakage if the generator is water cooled. A liquid detector located within this drain line provides a signal or alarm when fluid accumulates in the drain line. The operator or plant maintenance personnel then manually drain the drain line to remove the oil and water if present.
For various reasons beyond the control of the manufacturers of turbine-generators, operators and plant maintenance personnel sometimes fail to respond to such signals or alarms and do not empty the drain lines, which can result in forced outages, generator down time and possible generator damage.